02 June 2011

Fossils of a meter-long (3.3-foot) prehistoric ocean predator have been found in southeastern Morocco.

The specimens include the largest yet of its kind and suggests the spiny, somewhat shrimplike beasts dominated pre-dinosaur seas for millions of years longer than thought.

Early offshoots of an evolutionary line that led to modern crustaceans, the so-called anomalocaridids looked sort of like modern shrimp or cuttlefish. But the fossil creatures had spiny limbs sprouting from their heads and circular, plated mouths, which opened and closed like the diaphragm of a camera.

Previous anomalocaridid fossils had shown the animals grew to perhaps 2 feet (0.6 meter) long, which already would have made them the largest animals of the Cambrian period (542 to 501 million years ago)—an evolutionarily explosive time, when invertebrate life evolved into many new varieties, such as sea lilies and worms.

The new anomalocaridid fossils also gave scientists another shock: They're surprisingly young.

Dating back to "only" 488 to 472 million years ago, in the Ordovician period, the specimens hint that anomalocaridid species survived for 30 million years longer than previous evidence had suggested. (View a prehistoric time line.)

Anomalocaridids are widespread in fossils from the Cambrian, "then they disappear from the rock record at about 510 million years ago," said Briggs, who received funding from the National Geographic Society's Committee for Research and Exploration. (The Society owns National Geographic News.)